Multiple-laboratory comparison of in vitro assays utilized to characterize hematopoietic cells in cord blood

Assay optimization for the objective quantification of human multilineage colony-forming units

Colony-forming unit (CFU) assays are a powerful tool in hematopoietic research because they allow researchers to functionally test the lineage potential of individual stem and progenitor cells. Assaying for lineage potential is important for determining and validating the identity of progenitor populations isolated by methods such as fluorescence-activated cell sorting (FACS). However, current methods for CFU assays are limited in their ability to robustly assay multipotent progenitors with the ability to differentiate down the myeloid, erythroid, and megakaryocytic lineages because of the lack of specific growth factors necessary for certain lineage outputs. In addition, manual counting of colony types is subjective resulting in user to user variability in assessments of cell types based on colony and cell morphologies. We demonstrate that the addition of granulocyte colony-stimulating factor (G-CSF), macrophage (M)-CSF, and granulocyte-macrophage (GM)-CSF into a collagen-based MegaCult medium containing IL-3, IL-6, SCF, EPO, and TPO allows for the differentiation of common myeloid progenitors into expected proportions of colonies containing granulocytic (G), monocytic (M), erythroid (E), and megakaryocytic (Mk) cells. Additionally, we demonstrate an objective method using in situ immunofluorescence (IF) with anti-CD66b, anti-CD14, anti-CD235a, and anti-CD41 to detect G, M, E, and Mk cells, respectively. IF stained colonies can be analyzed individually at a microscope or using high-throughput microscopy. Thus, our improvements to the culture conditions and method for assay readout increase the accuracy, reproducibility, and throughput of the myeloid CFU assay.

Validation of a semi automatic device to standardize quantification of Colony-Forming Unit (CFU) on hematopoietic stem cell products

Accurate characterization of hematopoietic stem cells (HSC) products is needed to better anticipate the hematopoietic reconstitution and the outcome in patients. Although CD34+ viable cells enumeration is a key predictor of time to correction of aplasia, it does not fully inform about functionality of cells contained in the graft. CFU assay is the gold standard in vitro potency assay to assess clonogenicity of HSC and consists on the count and identification of colonies several days after culture in a semi solid media. Manual count of colonies with optic microscope is the most commonly used method but its important variability and subjectivity hinders the universal implementation of this potency assay. The aim of this study is to validate a standardized method using the STEMvision™ system, the first semi-automated instrument for imaging and scoring hematopoietic colonies, according to French and European recommendations. Results obtained highlight better performance criteria with STEMvision™ system than the manual method. This semi-automatic device tends to reduce the coefficients of variation of repeatability, inter-operator variability and intermediate precision. This newly available platform could represent an interesting option, significantly improving performances of CFU assays used for the characterization of hematopoietic progenitors.

Relevance of flow cytometric enumeration of post-thaw leucocytes: influence of temperature during cell staining on viable cell recovery

BACKGROUND AND OBJECTIVES

Our post-thaw cell recovery rates differed substantially in interlaboratory comparisons of identical samples, potentially due to different temperatures during cell staining.

MATERIALS AND METHODS

Viable CD34(+) cells and leucocyte (WBC) subtypes were quantified by multiparameter single-platform flow cytometry in leucapheresis products collected from 30 adult lymphoma and myeloma patients, and from 10 paediatric patients. After thawing, cells were prepared for analysis within 30 min between thawing and acquisition, at either 4°C or at room temperature.

RESULTS

For cell products cryopreserved in conventional freezing medium (10% final DMSO), viable cell recovery was clearly lower after staining at 4°C than at RT. Of all WBC subtypes analysed, CD4(+) T cells showed the lowest median recovery of 4% (4°C) vs. 25% (RT), followed by CD3, CD34 and CD8 cells. The recovery was highest for CD3γδ cells with 44% (4°C) vs. 71% (RT). In the 10 samples cryopreserved in synthetic freezing medium (5% final DMSO), median recovery rates were 89% for viable CD34 (both at 4°C and RT) and 79% (4°C) vs 68% (RT) for WBC.

CONCLUSIONS

The post-thaw environment and, potentially, the cryoprotectant impact the outcome of cell enumeration, and results from the analysis tube may not be representative of the cells infused into a patient.

Static image analysis as new approach for the characterization of tumor cell lysate used in dendritic cell vaccine preparation

BACKGROUND

Safety is an important consideration for the clinical application of dendritic cells (DC) loaded with autologous tumor lysate (TL). Thus, avitalization of TL from living autologous tumor tissue has to be guaranteed.

METHODS

Composition of TL was investigated by static image analysis (SIA) with the Morphologi G3 device, which simultaneously measures size and shape of up to 100,000 particles within one sample run. This approach was compared with sample characterization by high-resolution automated cell counting, trypan blue staining, and ATP quantification.

RESULTS

Using SIA, we only detected fragmented, non-cellular structures in completely avitalized TL, indicating complete destruction of living cells. Analysis of particle size distribution by SIA as well as CASY cell counter showed that 95% of particles had a diameter of <10 µm as a sign of cell fragmentation. Complete avitalization of TL was confirmed with trypan blue staining and ATP analysis.

CONCLUSION

Regarding generation of DC vaccines, the proof of avitality of TL from living tumor tissue can clearly be achieved by SIA alone or in combination with standard assays. Our data show that SIA is a highly precise method for TL characterization. The SIA device complies with FDA regulation and, therefore, might be suitable for characterization of cellular therapy medicinal products.

Dominant unit CD34+ cell dose predicts engraftment after double-unit cord blood transplantation and is influenced by bank practice

We investigated the unit characteristics associated with engraftment after double-unit cord blood (CB) transplantation (dCBT) and whether these could be reliably identified during unit selection. Cumulative incidence of neutrophil engraftment in 129 myeloablative dCBT recipients was 95% (95% confidence interval: 90-98%). When precryopreservation characteristics were analyzed, the dominant unit CD34(+) cell dose was the only characteristic independently associated with engraftment (hazard ratio, 1.43; P = .002). When postthaw characteristics were also included, only dominant unit infused viable CD34(+) cell dose independently predicted engraftment (hazard ratio, 1.95; P < .001). We then examined the determinants of infused viable CD34(+) cell dose (precryopreservation count, postthaw recovery, and postthaw viability) in 402 units thawed at our center. This revealed close correlation between precryopreservation and postthaw CD34(+) cell counts (r(2) = 0.73). Median CD34(+) cell recovery was 101%, although it ranged from 12% to 1480%. Notably, units from non-Netcord Foundation for the Accreditation of Cellular Therapy (Netcord-FACT)-accredited banks were more likely to have low recovery (P < .001). Furthermore, although median postthaw CD34(+) cell viability was 92%, 33 (8%) units had <75% viable CD34(+) cells. Units from non-Netcord-FACT-accredited banks and units with cryovolumes other than 24.5 to 26.0 mL were more likely to have poor postthaw viability. Precryopreservation CD34(+) cell dose and banking practices should be incorporated into CB unit selection.

Current practices and prospects for standardization of the hematopoietic colony-forming unit assay: a report by the cellular therapy team of the Biomedical Excellence for Safer Transfusion (BEST) Collaborative

BACKGROUND AIMS

Wide acceptance of the colony-forming unit (CFU) assay as a reliable potency test for stem cell products is hindered by poor inter-laboratory reproducibility. The goal of this study was to ascertain current laboratory practices for performing the CFU assay with an eye towards identifying practices that could be standardized to improve overall reproducibility.

METHODS

A survey to evaluate current laboratory practices for performing CFU assays was designed and internationally distributed.

RESULTS

There were 105 respondents to the survey, of whom 68% performed CFU assays. Most survey recipients specified that an automated rather than a manual cell count was performed on pre-diluted aliquots of stem cell products. Viability testing methods employed various stains, and when multiple sites used the same viability stain, the methods differed. Cell phenotype used to prepare working cell suspensions for inoculating the CFU assay differed among sites. Most respondents scored CFU assays at 14-16 days of incubation, but culture plates were read with various microscopes. Of 57 respondents, 42% had not performed a validation study or established assay linearity. Only 63% of laboratories had criteria for determining if a plate was overgrown with colonies.

CONCLUSIONS

Survey results revealed inconsistent inter-laboratory practices for performing the CFU assay. The relatively low number of centers with validated CFU assays raises concerns about assay accuracy and emphasizes a need to establish central standards. The survey results shed light on numerous steps of the methodology that could be targeted for standardization across laboratories.

[Quality control of defrosted cord blood units: results from an inter-laboratory study]

PURPOSE

Today, haematopoietic stem cell graft from placental blood concerns more than 15 % of allogeneic grafts. An inter-laboratory study of the quality control of defrosted cord blood units has been coordinated by the French society for cell and tissue bioengineering (SFBCT), with the cord blood bank of Bourgogne Franche-Comté and controlled by the French health products safety agency (Afssaps). The aim of this study is to ensure the inter-laboratory reproducibility of the quality controls practised by the banks during defrosting. The cellular outputs were analyzed according to the defrosting techniques, according to the method used in flow cytometry: single-platform (SP) versus double-platform (DP), or the product nature, i.e. in total blood or miniaturized.

METHODS

Forty-two units of placental blood (USP), which were out of range were provided for defrosting to 14 participating sites. USP were defrosted and controlled according to the procedures of each bank. Once the USP is defrosted, a part of the product was controlled by the site and the other part by Afssaps. Following controls were carried out: numeration of the total nucleated cells (TNC) and of CD34+ cells (made by a SP method in Afssaps) and functional assay.

RESULTS

Concerning TNC, the defrosting sites obtained a cellular output of 94 %+/-28 in day 0 compared with an output of 72 %+/-24 in Afssaps showing a rather good stability of the USP transmitted with an average deviation of 23 %+/-22. The freezing process with or without reduction of volume does not affect this variation. Concerning the numeration of CD34+ cells, the average deviation between the participating sites and Afssaps was 29 %+/-23 compared with 21 %+/-16 for the sites using a SP method against 47 %+/-25 for those using a DP method. The CD34+ outputs are equal to 82 % +/- 60 in day 0 for the participating sites against 52 %+/-20 for Afssaps. For the sites using a DP method, it is stressed that this output is particularly high with a rate of 126 %+/-90 (n=15) whereas it is 62 %+/-20 (n=32) for the sites using a SP method.

CONCLUSION

These results underline a good stability of viable CD34+ cells and a greater reliability of the SP methods for the CD34+ cell numeration for these defrosted USP. Lastly, the results of the functional assay regarding the average clonogenicities (equal to 15 %) reinforce the conclusions on the quality of the defrosted products.

Consistency of the initial cell acquisition procedure is critical to the standardization of CD34+ cell enumeration by flow cytometry: results of a pairwise analysis of umbilical cord blood units and cryopreserved aliquots

BACKGROUND

The CD34+ cell content is a predictive factor for engraftment and survival after umbilical cord blood (UCB) transplantation. The high variability in the CD34 assay results in different recommended cell doses for infusion across transplant centers and also limits the clinical utility of the CD34+ cell counts provided by cord blood banks (CBBs). This bi-institutional study was intended to understand the sources of this variability.

STUDY DESIGN AND METHODS

The level of CD34 agreement between the University of Minnesota (UM) and the Madrid CBB (MCBB) was evaluated on 50 UCB units before and after cryopreservation. Two cryopreserved vials per unit were thawed and processed at both laboratories. Dual-platform ISHAGE-based flow cytometry was used for CD34 enumeration.

RESULTS

Postthaw nucleated cell recoveries were similar. However, whereas CD34+ cell enumeration before freezing was 0.35 +/- 0.22 percent, the results after thawing were 0.98 +/- 0.65 and 0.57 +/- 0.39 percent at UM and MCBB, respectively. Bland-Altman plots analysis ruled out the interchangeability of MCBB and UM CD34 values. Differences in the initial cell acquisition settings accounted for most of the CD34 discrepancy, which was no longer present after normalization of the forward scatter threshold for cell acquisition.

CONCLUSIONS

The standardization of CD34+ cell enumeration by flow cytometry is strongly reliant on a consistent initial cell acquisition procedure. The interlaboratory variation can be minimized by using frozen cell aliquots as reference samples. Both requisites should be considered for CD34 testing and UCB unit selection by regulatory institutions involved with cord blood banking and transplantation.

Association of cord blood platelet characteristics and hematopoietic progenitor cells

BACKGROUND

Total nucleated cell (TNC) dose is associated with neutrophil and platelet (PLT) engraftment after cord blood (CB) transplantation and thus is used for selection of CB for banking. The goal of this study was to evaluate the internal relationships of CB PLT characteristics, TNC, and the hematopoietic progenitor cell (HPC) content of CB units.

STUDY DESIGN AND METHODS

HPC and TNC counts of 167 CB units processed with an automated cell separation system were compared with CB PLT count and mean PLT volume (MPV). Megakaryocyte progenitors (CFU-MK) were cultured from a subset of units (n = 24).

RESULTS

PLT concentration correlated with MPV (r = -0.39), which was also associated with both TNC and total CD34+ cells before and after processing (r = 0.37 and 0.35 and r = 0.41 and 0.42, respectively). In addition, MPV was associated with HPC counts in the CB unit. The p value was less than 0.001 for all associations. PLT count was inversely associated with markers of hematopoietic potential. Median removal of PLTs during processing was 62 percent (range, 40%-84%). All 24 CB units of the subset exhibited CFU-MK growth. In multivariate linear regression analysis, MPV improved prediction of the HPC content of the CB unit compared to prediction with CB volume and nucleated cell concentration only.

CONCLUSION

Mean PLT volume correlated with current markers of CB hematopoietic potential and is potentially useful for evaluating CB collections for banking. The question of the clinical significance of PLT characteristics in CB transplantation remains unanswered.

Loss of integrity of umbilical cord blood unit freezing bags: description and consequences

BACKGROUND

Umbilical cord blood (UCB) is now a commonly used resource for hematopoietic stem cell (HSC) transplantation; great effort has been put forth in standardizing protocols for processing, storage, and testing of UCB units. Because UCB units are selected on an individual basis to maximize the chance of engraftment, loss of container integrity may have adverse effects on patient outcome.

STUDY DESIGN AND METHODS

All bag breaks involving UCB units thawed for transplantation at our institution between January 1, 2000, and May 31, 2006, were identified. Information on various laboratory variables and the clinical consequences of UCB bag breaks was obtained from the deviation database of the Clinical Cell Therapy Laboratory (CCTL). Patient medical charts were reviewed for infusion-related data.

RESULTS

The incidence of bag breaks over a 6 1/2-year period was 3.5 percent. A majority of cases of loss of container integrity occurred in units that had been cryopreserved for more than 2 years (75%) and resulted in minimal loss of product. There were no significant decreases in quantity or quality of UCB, as determined by various quality control tests; no adverse clinical outcomes related to receiving a broken UCB unit were noted except increased antibiotic usage.

CONCLUSION

There was a relatively low incidence of UCB bag breaks in this study that did not result in significant loss of UCB or adverse clinical outcomes. With the FDA considering licensure of UCB for hematopoietic reconstitution, improvement in container design and possibly guidelines limiting length of storage will likely be addressed in detail.

Development of a novel assay to evaluate the functional potential of umbilical cord blood progenitors

BACKGROUND

Although the colony-forming cell (CFC) assay provides the most relevant information regarding the functional potential of progenitors in a unit of umbilical cord blood (UCB), technical challenges associated with this assay have made it difficult to standardize the assay among testing laboratories. The purpose of this study was to assess the reproducibility of a newly developed functional assay (HALO SPC-QC [HALO], HemoGenix, Inc.). This test is based on the principle that cellular proliferation responses to cytokine stimuli are proportional to intracellular ATP levels from progeny cells generated in culture from progenitors.

STUDY DESIGN AND METHODS

Results of the HALO assay were evaluated at two geographically distinct sites with matched aliquots from 12 different UCB units.

RESULTS

A significant correlation between the two sites for total nucleated cell counts was observed (r = 0.98, p < 0.001). Similarly, a strong correlation between HALO results from both sites was observed (r = 0.94, p < 0.001). Also, despite using different methods at each site for the CFC assay, results from the two sites correlated (r = 0.79, p = 0.002). A good correlation between the CFC and HALO assays (r = 0.73, p < 0.005), however, was only observed at the site with the same cytokine cocktail for both the CFC and the HALO assays.

CONCLUSION

These results support the notion that the HALO assay is a reasonable approach for measuring the functional potential of hematopoietic progenitors in UCB. Moreover, because the final readout for the HALO assay is instrument based, unlike the CFC assay, which requires a subjective enumeration of colonies, the HALO assay may be more amenable to standardization.

Multicenter study on in vitro characterization of dendritic cells

BACKGROUND

There is growing interest in the use of in vitro-expanded dendritic cells (DC) in cancer immunotherapy as cellular-based vaccines. However, the methods used for in vitro preparation vary widely between institutions. Therefore, a strong need exists for standardization, characterization and quality control (QC) of such vaccines. A first prospective multicenter pilot study was performed to investigate basic QC parameters of frozen/thawed DC. The study design was focused on comparison of test results for cell counts, immunophenotyping and cell viability.

METHODS

CD14+ monocytes were isolated from three healthy volunteers. The cells were expanded in vitro, matured and cryopreserved using a standardized protocol in one laboratory. The aliquots of cryopreserved DC and a panel of reagents were shipped to eight laboratories worldwide. The objective was to compare the results of non-functional QC assays between sites by testing identical DC vaccines and using a pre-defined test protocol.

RESULTS

Measurements of nucleated cell (NC) content of thawed DC vaccines with different types of hematology analyzers (HA) gave similar results for the majority of sites. Immunophenotyping using identical clones of monoclonal antibodies for the detection of surface antigens (i.e. CD1a, CD14, CD16, CD83, CD86 and HLA-DR) provided mostly comparable results between laboratories with an acceptable level of variation. In contrast, highly different results between study sites were generated for measuring the viability of thawed DC by flow cytometry using 7-amino-actinomycin D (7-AAD) dye exclusion.

DISCUSSION

In characterizing frozen/thawed DC vaccines, NC counts generated by HA yielded similar results between different laboratories. Furthermore, immunophenotyping of DC vaccines can be standardized between centers, i.e. by using identical reagents. Because of highly variable results between laboratories, 7-AAD viability testing of thawed DC needs to be studied further to identify potential causes for the observed variability.

Assessment of cord blood hematopoietic cell parameters before and after cryopreservation

BACKGROUND

The testing of cord blood (CB) progenitor and stem cell units for transplantation suitability involves enumeration of total nucleated cells before freezing. CD34+ cell counts may also be a means of determining suitability. Studies have been conducted to evaluate how specific storage conditions influence cell counts.

STUDY DESIGN AND METHODS

CB units were processed by hydroxyethyl starch volume reduction. Cryopreserved-thawed samples were diluted 1:3 without washing. CD34+ cells were measured with three commercially available assay methods. In specific studies, apoptosis-indicating reagents were included. CB units were analyzed for nucleated cells, aldehyde dehydrogenase-containing cells, and progenitor colonies.

RESULTS

CD34+ cell levels and nucleated cells were retained during storage in test tubes at 1 to 6 degrees C for 3 days. Cryopreserved-thawed samples showed a reduction in CD34+ cells relative to prefreeze levels with the largest decrease with the Stem-Kit (Beckman Coulter) restricted gating procedure. Prefreeze samples contained minimal numbers of presumed apoptotic cells detected with 7-aminoactinomycin D or SYTO16, but after cryopreservation-thawing there was an increase. Nucleated cell levels determined with a hematology analyzer or flow cytometry were reduced after thawing. Cryopreservation-thawing reduced the percentage of CD34+ cells positive for the presence of aldehyde dehydrogenase and the number of progenitor colonies. These differences were significant.

CONCLUSION

These studies indicate that CD34+ cell counts were maintained when CB samples were stored at 1 to 6 degrees C in test tubes for 3 days. Cryopreservation-thawing resulted in changes in a number of parameters including the percentage of CD34+ cells that were aldehyde dehydrogenase(+) and the number of 7-aminoactinomycin D(+) cells and SYTO16(low) cells.

CD34+ progenitors are reproducibly recovered in thawed umbilical grafts, and positively influence haematopoietic reconstitution after transplantation

Cord blood (CB) units are increasingly used for allogeneic transplantation. Cell dose, a major factor for CB selection, is evaluated before freezing by each CB bank, using various techniques. This may introduce variability and affect the prediction of cell recovery after thawing, or haematopoietic reconstitution. Forty-two children were transplanted at the same institution with unrelated CB units. All units were thawed and evaluated at the same cell therapy facility, using standard procedures. We investigated: (i) factors that affect cell loss after thawing, and (ii) the importance of CD34(+) cell doses. Prefreeze and post-thaw CD34(+) cell doses were statistically correlated, thus suggesting that variability in numeration techniques used by different CB banks does not compromise the biological and clinical value of these figures. CD34(+) cell recovery appeared to be correlated with the absolute number of CD34(+) cells per frozen bag. Infused CD34(+) is the cell dose that better correlates with platelet reconstitution delay; in addition, when using a quartile comparison, haematopoietic recovery appeared to be related with prefreeze and post-thaw CD34(+) cell doses. We conclude that enumeration of CD34(+) cells in CB units is of biological significance, and may help select CB units and identify patients at risk of delayed recovery.

Multi-laboratory evaluation of procedures for reducing the volume of cord blood: influence on cell recoveries

BACKGROUND

Various procedures can be used to isolate stem and progenitor cells from cord blood. This study evaluated the hydroxyethyl starch sedimentation (HES) with two centrifugation steps, and the top and bottom (T&B) isolation of buffy coat following a single centrifugation, and two filter systems for processing cord blood, one developed by Asahi Kasei Medical (filter A) and the second by Terumo (filter B).

METHODS

Each of seven laboratories was randomly assigned the evaluation of either the HES or T&B method and one of the filter methods (n=8 cord blood units, per laboratory, for each method). The leukocyte-containing fraction with the stem/progenitor cells was recovered from the filters by reverse flushing. Utilizing the routine traditional processing and testing procedures of each laboratory, in vitro parameters were determined, with samples obtained after collection, after processing and after freezing/thawing. The results were expressed as the percentage recovery of viable cells in processed vs. collected samples (performance 1; PF1) and in thawed vs. processed samples (performance 2; PF2). The composite results obtained by the seven laboratories were summarized.

RESULTS

The median PF1 percentage recovery of total nucleated cells (TNC) was comparable with both traditional methods (HES 79%, T&B 86%) and statistically reduced with both filtration procedures (filter A 58%, filter B 61%). Mononuclear cell (MNC) PF1 recovery was highest statistically with the T&B method (91%) and reduced on using filter A (77%) and filter B (70%) and the HES method (72%). CD34+ cell recovery was judged to be essentially comparable with the four methods, although the range of unit recoveries differed. The percentage recovery of TNC and MNC in PF1 was influenced by the volume of the collected cord blood, especially with use of the filtration procedures. This correlated with TNC content. A greater percentage of red cells and platelets was removed during processing with both filter methods. The time to process cord blood preparations with filter A was significantly shorter than the other methods. Processing with the HES method took the longest time. The recoveries for TNC, MNC and CD34+ cells in PF2 did not appear to be influenced by the specific processing procedure.

DISCUSSION

These data indicate that filters that capture stem and progenitor cells may be an appropriate methodology for processing cord blood collected for banking.